Polyester film for forming printed circuit

Abstract

A polyester film for printed circuits to be used as a base in a printed circuit base plate or as a base and/or cover layer in a printed circuit board, which undergoes a degree of dimensional stability of not more than 1% in both the longitudinal and transverse directions when kept at 150° C. for 30 minutes, and which is obtained by heat treating an extrusion molded and stretched polyester film at 150° C. to 240° C. without applying tension.

What is claimed is: 
     
       1. A polyester film for printed circuits to be used as a base in a printed circuit base plate or as a base and/or cover layer in a printed circuit board, which undergoes a degree of dimensional stability of not more than 1% in both the longitudinal and transverse directions when kept at 150° C. for 30 minutes, and which is obtained by heat treating an extrusion molded and stretched polyester film at 150° C. to 240° C. without applying tension, wherein said extrusion molded and stretched film is a polyethylene terephthalate film, and wherein said polyester film has a refractive index of 1.4990 or more, measured by an Abbe refractometer, in the thickness direction. 
     
     
       2. The polyester film for forming printed circuits as claimed in claim 1, which has a heat resistant adhesive layer on one side thereof.